U.S. patent application number 10/923577 was filed with the patent office on 2005-03-24 for gas offloading system.
Invention is credited to Pollack, Jack, Wille, Hein.
Application Number | 20050061395 10/923577 |
Document ID | / |
Family ID | 34317490 |
Filed Date | 2005-03-24 |
United States Patent
Application |
20050061395 |
Kind Code |
A1 |
Pollack, Jack ; et
al. |
March 24, 2005 |
Gas offloading system
Abstract
A system is described for offloading LNG (liquified natural gas)
from a tanker for eventual delivery to an onshore gas distribution
station. The system includes a floating structure that floats at
the sea surface and that is connected to the tanker so they
weathervane together. The floating structure carries a regas unit
that heats the LNG to produce gas, and delivers the gas through a
riser to an underground cavern that stores the gas. Gas from the
cavern is delivered through a seafloor pipeline to an onshore gas
distribution station. The regas unit includes water pumps and other
equipment that is powered by electricity. The electricity can be
obtained from an electric generator on the floating structure, with
surplus electricity delivered through a sea floor electric power
line that extends along the sea floor to an onshore electricity
distribution facility. The electricity can instead be obtained by
delivery from an onshore facility though a sea floor electric power
line that extends up to the floating structure and to the regas
unit.
Inventors: |
Pollack, Jack; (Houston,
TX) ; Wille, Hein; (Eze, FR) |
Correspondence
Address: |
LEON D. ROSEN
FREILICH, HORNBAKER & ROSEN
Suite 1220
10980 Wilshire Blvd.
Los Angeles
CA
90024
US
|
Family ID: |
34317490 |
Appl. No.: |
10/923577 |
Filed: |
August 20, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60504449 |
Sep 19, 2003 |
|
|
|
60515767 |
Oct 30, 2003 |
|
|
|
Current U.S.
Class: |
141/388 |
Current CPC
Class: |
F17C 2223/033 20130101;
F17C 2270/0142 20130101; F17C 2225/035 20130101; F17C 2270/0149
20130101; F17C 2227/0157 20130101; F17C 2223/0161 20130101; F17C
9/00 20130101; F17C 9/02 20130101; F17C 2270/0105 20130101; F17C
2270/016 20130101; F17C 2225/0161 20130101; F17C 2270/0123
20130101; B63B 21/50 20130101; F17C 2270/0163 20130101; F17C
2227/0393 20130101; F17C 2270/0155 20130101; F17C 2227/0318
20130101; B63B 27/24 20130101; F17C 2225/036 20130101; F17C
2270/0113 20130101; F17C 2270/0126 20130101; F17C 2270/0136
20130101; F17C 2221/033 20130101; F17C 2225/0123 20130101; F17C
2265/05 20130101 |
Class at
Publication: |
141/388 |
International
Class: |
F17C 009/02 |
Claims
What is claimed is:
1. An offshore gas unloading system that lies in a sea having a sea
surface and a sea floor, wherein a tanker unloads liquified cold
hydrocarbons that are gaseous at room temperature, comprising: a
floating structure that lies at the sea surface and that is moored
so it weathervanes; a regas unit on said floating structure, that
heats at least some of the cold hydrocarbons that were received
from the tanker; a sea floor platform that lies at the sea floor; a
riser that extends from said floating structure to said sea floor
platform to carry hydrocarbons from one to the other; said floating
structure being connected to said tanker to form a combination of
said floating structure and said tanker that weathervane together;
at least one mooring line that extends from the sea floor to said
combination to moor the combination and allow it to weathervane; an
underground cavern and a pipe that is coupled to said cavern and to
said riser, to thereby store at least some of the gas in the
cavern.
2. The system described in claim 1 including: an onshore gas
distribution station; a seafloor pipeline that is coupled to said
cavern and that extends primarily along the sea floor from said
cavern to said onshore station to carry said gas from said cavern
to said onshore station;
3. The system described in claim 1 including: an onshore gas
distribution station; a second riser extending from said floating
structure to sea floor; a sea floor pipeline that extends primarily
along the sea floor from a lower end of said second riser to said
onshore station, whereby to enable the passage of gas into said
cavern or directly to said onshore station without passing through
said cavern.
4. The system described in claim 1 including: an onshore gas
distribution station; said riser comprises a cryogenic hose, and
including a connection that carries some of the cold hydrocarbons
received by the floating structure, directly to the cavern without
passing through said regas unit so liquid cold hydrocarbons pass
down through said cryogenic hose; said cavern has upper and lower
portions, and including a sea floor gas pipeline that has a
proximal end coupled to said cavern upper portion to receive gas
therefrom, said pipeline extending to said onshore station.
5. The system described in claim 1 wherein: said regas unit is
electrically energized; and including an electric generator
apparatus mounted on said floating structure, which is fueled by
gas from said regas unit and that generates electricity to energize
said regas unit.
6. The system described in claim 5 including: an onshore electric
power distributing facility; an electric current-carrying power
line extending from said electric. generator apparatus to the sea
floor and along the sea floor to said onshore facility for carrying
power to said onshore facility when such power is not required at
the floating structure.
7. The system described in claim 1 wherein: said regas unit is
electrically energized; and including an onshore power distributing
facility; an electric current-carrying power line that extends
along the sea floor from said onshore facility to a location under
said floating structure and up through the sea to said floating
structure to carry electric power to said regas unit.
8. An offshore gas unloading system that lies in a sea that has a
sea floor and a sea surface, and that lies within about fifty
kilometers of a shore, for unloading cold hydrocarbons from a
tanker, comprising: a floating structure that lies at the sea
surface and that has a fluid coupling for receiving said liquid
cold hydrocarbons from said tanker; a cavern that stores gas; a sea
floor platform and at least one pipe that extends from said sea
floor platform to said storage facility; at least one riser that
extends from said floating structure to said sea floor platform and
that is coupled to said pipe to carry hydrocarbons between said
sea-surface structure and said cavern; said floating structure
carrying an electrically powered equipment including a regas unit;
an electric power facility that lies on the shore; a current
carrying power line that extends between said sea-surface structure
and said electric power facility on the shore, to carry electricity
between them.
9. The system described in claim 8 including: an electricity
generator mounted on said floating structure that supplies
electricity to said equipment, and an electric switch arrangement
that delivers electricity from said generator to said power line
when much of the electricity is not required for said
equipment.
10. The system described in claim 8 wherein: said electric power
facility that lies on the shore is constructed to deliver
electrical power to said power line, to provide electrical power to
energize said equipment.
11. The system described in claim 8 wherein: said storage facility
comprises an underground cavern that is connected to an end of said
pipe that is opposite said riser; and including a gas-powered
electricity generator on said floating structure; a valve
arrangement that is operable to pass said gas from said regas unit
through said riser and pipe to said cavern, and to pass gas from
said cavern through said pipe and said riser to said electricity
generator, whereby the cavern stores gas to power the electricity
generator.
12. A gas offloading system that lies off shore in a sea, for
receiving cold liquified gaseous hydrocarbons from a tanker,
comprising: an offshore structure that lies at the sea surface and
that has a coupling for receiving said liquified hydrocarbons from
the tanker; a regas unit mounted on said offshore structure to heat
said cold hydrocarbons to produce gas; an electric power-generating
facility on said offshore structure that is powered by said gas and
that produces electricity; an onshore power facility that
distributes electric power; a current carrying power line that
extends between said electric power-generating facility and said
onshore power facility to carry electricity from said
power-generating facility to said onshore power facility.
13. The system described in claim 12 wherein: said regas unit
consumes electric power in the heating of said cold gas, and
including a switch arrangement that directs electricity from said
electric power-generating facility to said regas unit to heat cold
gas when such cold gas is received from a tanker, said switch
arrangement being switchable to direct electricity from said
electric power-generating facility to said power line when the
regas unit is not operated to heat cold gas.
14. A method for operating an offshore facility that lies off
shore, and that unloads cold hydrocarbons from a tanker, for
delivery of the hydrocarbons after warming, to a shore station on
the shore, comprising: offloading cold hydrocarbons from the tanker
to a floating structure that has a regas unit, and passing said
cold hydrocarbons through said regas unit to produce warmed gaseous
hydrocarbons; flowing at least some of said warmed gaseous
hydrocarbons down along a riser to an underground cavern and
storing said warmed hydrocarbons in the cavern; flowing gaseous
hydrocarbons through a sea floor pipeline from said cavern to an
onshore gas distribution station.
15. The method described in claim 14 including: flowing a second
portion of said warmed gas down along a riser directly to said sea
floor pipeline so said second portion of the gas flows to the
onshore station without having first passed into said cavern.
16. The method described in claim 14 including: energizing said
regas unit with electricity, including using some of said warmed
gaseous hydrocarbons to fuel an electrical generator apparatus on
said floating structure to generate electric power to energize said
regas unit; delivering electricity from said electrical generator
apparatus along a sea floor electric power line to an onshore
facility when excess electric power is available from said electric
generator apparatus.
17. The method described in claim 14 including: energizing said
regas unit with electricity; delivering electricity from an onshore
facility along a sea floor electric power line to said floating
structure to energize said regas unit with electric power from the
onshore facility.
18. A method for operating an offshore facility that lies off
shore, and that unloads liquid cold hydrocarbons from a tanker, for
delivery of the hydrocarbons as gas after warming, to a shore
station on the shore, comprising: offloading cold liquid
hydrocarbons from the tanker to a floating structure that has a
regas unit, energizing said regas unit and passing said cold
hydrocarbons through said regas unit to produce warmed gaseous
hydrocarbons; flowing at least some of said warmed gaseous
hydrocarbons down along a riser, and flowing warmed gaseous
hydrocarbons through a sea floor pipeline to an onshore gas
distribution station; said step of energizing said regas unit
includes using some of said warmed gaseous hydrocarbons as fuel to
energize an electricity generating apparatus on said floating
structure that generates electricity, and supplying at least some
of said electricity from said electricity generating apparatus to
said regas unit to energize it; passing some of said electricity
from said electric generating apparatus through an electric power
line that extends along the sea floor, to an onshore power
distribution station.
19. A method for operating an offshore facility that lies off
shore, and that unloads cold liquid hydrocarbons from a tanker, for
delivery of the hydrocarbons after warming, to a shore station on
the shore, comprising: offloading cold hydrocarbons from the tanker
to a floating structure that has a regas unit, energizing said
regas unit and passing said cold hydrocarbons through said regas
unit to produce warmed gaseous hydrocarbons; flowing at least some
of said warmed gaseous hydrocarbons down along a riser, and flowing
warmed gaseous hydrocarbons through a sea floor pipeline to an
onshore gas distribution station; said step of energizing said
regas unit includes carrying electric power from an onshore
facility and along an electric power line that extends along the
sea floor and up to said floating structure to said regas unit to
energize said regas unit with electric power from the shore.
Description
CROSS REFERENCE
[0001] Applicant claims priority from U.S. Provisional application
Ser. No. 60/504,449 filed 19 Sep. 2003 and Ser. No. 60/515,767
filed 30 Oct. 2003.
BACKGROUND OF THE INVENTION
[0002] Hydrocarbons that are in a gaseous state at atmospheric
pressure and room temperature (e.g. 20.degree. C.), are often
transported as cold hydrocarbons, as by ship in liquid form such as
LNG (liquified natural gas), at atmospheric pressure and
-160.degree. C. Another form of cold gaseous hydrocarbons that are
ship-transported are hydrates (gas entrapped in ice). At the ship's
destination, the LNG (or other gas) may be heated and flowed to an
onshore distribution facility. Proposed prior art offloading
stations have included a fixed platform extending up from the sea
floor to a height above the sea surface and with a regas unit on
the platform for heating the LNG. Because of fire dangers in
dealing with LNG, rigid platforms, which minimize flexing joints,
have previously been proposed for offloading LNG from a tanker and
heating it to gassify it.
[0003] The cost of a fixed platform is high even at moderate
depths, and at increasing depths (e.g. over 50 meters) the costs of
fixed platforms increase dramatically. In addition, if the platform
lies in an open sea it is difficult to moor a tanker to the
platform because the tanker shifts position and heading with
changing winds, waves and currents. An offshore LNG offloading and
regas station which avoided the use of fixed platforms, and which
provided the high reliability demanded in LNG offloading, heating
and storage, would lower the cost of such stations and allow them
to be used in situations where they previously were
uneconomical.
SUMMARY OF THE INVENTION
[0004] In accordance with one embodiment of the present invention,
a relatively low-cost system is provided for offloading cold
hydrocarbons, and especially LNG (liquified natural gas), and
transporting the gas to an onshore gas distribution station. The
system includes a floating structure such as a barge at the sea
surface that is moored so it weathervanes. A tanker carrying LNG
attaches itself to the floating structure so they weathervane
together. A regas unit which heats the LNG, usually by transferring
heat from sea water, transforms the LNG into gas that can be more
easily passed through moderate cost hoses or pipes and eventually
to the onshore distribution station.
[0005] A new tanker arrives at the floating structure perhaps every
week, and efforts are made to offload the tanker as fast as
possible, perhaps in one day. To provide a steady flow of gas to
the onshore distribution station, much of the rapidly-offloaded and
regased LNG is stored in an underground (and usually undersea)
cavern. The gas is slowly flowed from the cavern along a seafloor
pipeline to the onshore distribution station, to provide a steady
gas supply without requiring a large gas storage facility at the
onshore station.
[0006] The regas unit and pumps for pressurizing gas, are
preferably electrically energized for safety and convenience.
Electric power on the order of 60 megawatts may be required. Such
electrical energy can be obtained from a power generator apparatus
on the floating structure that uses gas from the tanker for fuel.
The regas unit may require electric power only part of the time,
such as one day per week when LNG is being offloaded and regassed.
The rest of the time (e.g. several days per week) electric power
from the power generator apparatus is passed through a seafloor
electric power line to an onshore electric distribution facility.
The generation of electric power at the floating structure is
economical because the gas fuel is already available and because a
large amount of expensive land is not required to isolate the power
generation apparatus from onshore homes and businesses for
safety.
[0007] Electric power instead can be obtained from an onshore
electric power distribution facility. In that case, an electric
power line extends from the onshore facility and along the sea
floor and up to the floating structure.
[0008] The novel features of the invention are set forth with
particularity in the appended claims. The invention will be best
understood from the following description when read in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a partially sectional side view of an offshore gas
offloading and transfer system of a first embodiment of the
invention.
[0010] FIG. 1A is a plan view of a portion of the system of FIG.
1.
[0011] FIG. 1B is a plan view of a portion of a system that is a
variation of FIG. 1A.
[0012] FIG. 2 is a partially sectional side view of an offshore gas
offloading and transfer system of another embodiment of the
invention.
[0013] FIG. 3 is a partially sectional side view of an offshore gas
offloading and transfer system of another embodiment of the
invention.
[0014] FIG. 4 is a partially sectional side view of an offshore gas
offloading and transfer system of another embodiment of the
invention.
[0015] FIG. 5 is a partially sectional side view of an offshore gas
offloading and transfer system of another embodiment of the
invention.
[0016] FIG. 6 is a top isometric view of an offshore gas offloading
and transfer system of another embodiment of the invention.
[0017] FIG. 7 is a sectional side view of the system of FIG. 6.
[0018] FIG. 8 is a sectional side view of an offshore gas
offloading and transfer system of another embodiment of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] FIG. 1 illustrates an offloading and transfer station 10
that includes a weathervaning floating structure in the form of a
single barge 12 (there could be more than one barge) that floats at
the sea surface 15. The barge receives LNG through a coupling 15
and a loading arm 11 extending from midship of a tanker 13. The
barge is moored to the seafloor 14 by chains 16 extending from a
turret 20 mounted at the bow of the barge. The illustrated chains
extend in catenary curves to the seafloor and along the seafloor to
anchors. Preferably, the tanker is moored to the barge and they
weathervane together. This allows the barge and tanker to move in
unison and therefore remain close together in an open sea. A regas
unit 22 (for heating LNG to produce gas) and an injection unit 24
for pumping the LNG or gas to a high pressure, are both located on
the barge, and are used for injection of gas into an underground
cavern 30 that lies under the sea. The regas unit usually transfers
heat from seawater to the LNG to change it into gas. A flexible
riser 32 (there often can be two or more) extends up from a
platform 34 on the seafloor to the barge. The platform is connected
through a pipe 36 to the cavern 30 in which the pressured gas is
stored, that results from heating LNG. A pipeline 40 extends
primarily along the sea floor to an onshore gas distribution
station 42. The onshore station can be a gas grid that distributes
the gas to users, can be a power plant that distributes the gas to
gas turbines, etc.
[0020] The flexible riser 32 and connections 50, 52 at its opposite
ends, can be made highly reliable. In addition, reliable shutoff
valves are present at 54 on the platform and on the barge. During
the past forty years or so, large numbers of flexible risers have
been designed, constructed and used in offshore installations to
produce hydrocarbons (usually including gas and liquid) from
undersea reservoirs. Experience gained from such use has resulted
in high reliability. By using such reliable flexible risers and
shutoff valves in the present floating offloading and injection
station, applicant is able to achieve the same high standards of
reliability previously achieved with fixed platforms, but at far
lower cost.
[0021] FIG. 1A shows the tanker 13 and barge 12 held together to
weathervane together about the turret axis 56. FIG. 1B shows the
tanker moored to the barge by a hawser 60, so they weathervane
together.
[0022] FIG. 2 shows an offloading/injection station 70 similar to
that of FIG. 1, except that two risers 72, 74 are shown. One riser
72 connects to a pipe 76 that extends to the cavern 30. The other
riser 74 connects directly to a sea floor pipeline 80 that extends
to the onshore station 82. A break is indicated at 83 to indicate
that the pipeline may be long (e.g. over one kilometer). A pressure
boosting unit 84 on the barge 90 can pressurize gas that is pumped
through the pipeline 80. Such pressured gas is directed through
valves in the onshore station 82 but the gas does not have to be
pressurized by the onshore station. This keeps the pumps at 84 far
from any inhabited structures on shore.
[0023] During regasification of LNG on a vessel and offloading of
gas from the vessel, some of the offloaded gas is injected via
riser 72 into the cavern 30 while other gas is transferred through
riser 74 to the shore station. When no LNG is being offloaded, gas
is removed from the cavern via the riser 72, its pressure is
boosted by pressure boosting unit 84, and sent to the shore station
via riser 74. Thus, riser 72 is used bi-directionally.
[0024] FIG. 3 shows a system 100 in which the barge 102 injects LNG
directly into the cavern through a cryogenic pipeline or flexible
pipe 104. In the cavern 106 the LNG gradually changes into its gas
phase. Gas is withdrawn through a separate pipe 112 leading from an
upper portion of the cavern to a sea floor pipeline 110 that
extends to an onshore station 114.
[0025] In FIG. 4, all gas from the barge passes through a seafloor
pipeline 120 to an onshore station 122 that injects it into a
cavern 124 that is directly connected to the onshore station.
[0026] In FIG. 5, cold LNG is pumped from the barge 130 through a
cryogenic hose or pipeline riser 132, and passes through a
cryogenic seafloor pipeline 134 directly into an onshore injector
and regas unit 136 that connects through pipe 138 to the cavern
140. The injector 136 can inject LNG or can regas some or all of
the LNG before injection, depending upon the expected rate of gas
withdrawal and the amount already stored in the cavern. Gas is
removed from the cavern through a separate pipe 142 leading to
another onshore station 144.
[0027] FIG. 6 illustrate another offloading station 150 for
offloading gaseous hydrocarbons from a tanker 152. The tanker 152
carries the hydrocarbons as LNG at -165.degree. C. and atmospheric
pressure. The station includes a direct-attachment floating
structure 154. The direct-attachment floating structure includes a
buoyancy-adjusting floating system 160 and a propulsion system 162
that allows the floating structure to lie low in the water, slowly
propel itself until its under-tanker part 164 lies under the
tanker, and then deballast itself (by emptying water from ballast
tanks) until its parts 164, 166 engage the tanker. Such a structure
has been previously used in offloading crude oil from tankers.
[0028] The particular floating structure 154 of FIG. 6 also
includes a regas system 170 that warms the LNG so it becomes
gaseous. The floating structure pumps the gaseous hydrocarbons
through a riser 172 into a subsea cavern and/or through a pipeline
to a shore station. By regasing LNG, applicant avoid the need to
provide a cryogenic riser which may be very expensive.
[0029] FIG. 6 shows that a seafloor base 174 carries a fluid swivel
176. A hawser 180 that extends from a yoke 182 attached to the
swivel, extends to the bow 184 of the tanker to moor the tanker so
it weathervanes. The structure 154 weathervanes with the
tanker.
[0030] Energy is required to power the propulsion and ballast
systems, as well as the regas systems. The regas system will use
pumped seawater, as to warm an intermediate liquid that warms LNG
or even to directly warm the LNG to produce hydrocarbons in a
gaseous state. The hydrocarbons are pumped into a cavern 191 (FIG.
7) and/or a sea floor gas pipeline 190 that extends to an onshore
gas facility 192. Where the floating structure lies near shore
(e.g. not much more than fifty kilometers from shore), power can be
obtained from a power line 194 shown in FIG. 7. The power line
preferably extends parallel to the pipeline. The shore end 196 of
the power line can be connected to an on shore electric power
facility such as a utility electric line 200, or to a special shore
based power station. The floating structure shown in FIG. 6 as well
as FIGS. 1-5, may consume on the order of magnitude of 60 megawatts
of electricity when unloading a tanker. A power line to shore is
most practical when the seafloor base lies within about fifty
kilometers (less than 70 km) of shore so there are only moderate
power losses along the power line. The power line preferably lies
partially on the sea floor. In most cases the floating structure
lies at least 50 meters from shore in its greatest excursion, and
the seafloor platform lies at least 50 meters from shore (high
tide).
[0031] It is also possible to provide a small power plant,
indicated at 200 in FIG. 7, which uses a portion of the warmed gas
as fuel to continually produce electric power. The power is used
perhaps one day in five or seven primarily to pump sea water in the
heat exchanger and to pressurize gas. During the other 4 days out
of 5 or 6 days out of 7, the power is sent to shore along the power
line 194.
[0032] FIG. 8 illustrates a system 210 which includes a floating
structure 212 that is moored through its turret 214 to the sea
floor. A riser (one or more risers) 216 carries gas to a seafloor
reservoir 220 and to a pipeline 222 that extends along the sea
floor to shore. An electric power line 224 that extends primarily
along the sea floor, extends from the turret and over a buoy 226
and along the sea floor 226 to a facility on shore. The floating
structure carries a gas-powered generator 230 that generates
electricity for regasing (heating) LNG from a tanker (not shown) as
by pumping sea water through a heat exchanger, and for pressurizing
the gas. When not regasing or pumping, a switch arrangement 232
diverts the generated electric power through line 224 to an onshore
facility, as to add to electricity generated by a local electric
utility. Electricity can instead be transferred from a local
utility to the power line to power equipment.
[0033] In environments that are subject to occasional harsh weather
conditions such as a heavy storm or hurricane, the riser can be
constructed to be disconnected from the floating structure, and
laid down on the sea floor or floated in a submerged position. The
floating structure can be disconnected from the riser and from its
mooring system, and can be towed away, to be later reinstalled.
[0034] Thus, the invention provides a gas offloading and transfer
system for transferring gas from a tanker (wherein the gas is
stored in a liquid-like state such as LNG) to an undersea or
underground cavern and/or to the shore. The system can be
constructed at moderate cost even when it must lie in a sea of
considerable depth. The system includes a floating structure such
as a barge, which is moored, as by catenary chains, to the
seafloor. In most cases the floating structure is moored so it
weathervanes, to change direction so as to always face the sea in
the direction of least resistance. A tanker that brings the gas to
the barge is moored to weathervane with the floating structure, so
the tanker and floating structure can remain attached to one
another during offloading in the open sea. A weathervaning tanker
could not be easily moored to a fixed platform in an open sea. In
one system, the floating structure is a weathervaning barge. In
another system, the floating structure is a direct attachment
floating structure that, by itself, may not have a bow end that
turns to always faces upwind, but which attaches to a tanker that
is moored and thereby weathervanes with the tanker. An electric
current-carrying power cable can extend between the floating
structure and a shore-based electric power structure, to deliver
electric power to the floating structure to energize pumps and
other equipment, or to carry electricity from a power plant on the
floating structure to shore when not used at the floating
structure.
* * * * *